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handle when SeekEnd with -offset > max offset #63

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handle when SeekEnd with -offset > max offset #63

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8a96cfc
handle when SeekEnd with offset < - max offset
hirosumee Dec 20, 2023
7b3e262
override with negative value
hirosumee Dec 22, 2023
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45 changes: 31 additions & 14 deletions tail.go
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Original file line number Diff line number Diff line change
Expand Up @@ -2,11 +2,11 @@
// Copyright (c) 2015 HPE Software Inc. All rights reserved.
// Copyright (c) 2013 ActiveState Software Inc. All rights reserved.

//nxadm/tail provides a Go library that emulates the features of the BSD `tail`
//program. The library comes with full support for truncation/move detection as
//it is designed to work with log rotation tools. The library works on all
//operating systems supported by Go, including POSIX systems like Linux and
//*BSD, and MS Windows. Go 1.9 is the oldest compiler release supported.
// nxadm/tail provides a Go library that emulates the features of the BSD `tail`
// program. The library comes with full support for truncation/move detection as
// it is designed to work with log rotation tools. The library works on all
// operating systems supported by Go, including POSIX systems like Linux and
// *BSD, and MS Windows. Go 1.9 is the oldest compiler release supported.
package tail

import (
Expand All @@ -16,15 +16,17 @@ import (
"io"
"io/ioutil"
"log"
"math"
"os"
"strings"
"sync"
"time"

"gopkg.in/tomb.v1"

"github.com/nxadm/tail/ratelimiter"
"github.com/nxadm/tail/util"
"github.com/nxadm/tail/watch"
"gopkg.in/tomb.v1"
)

var (
Expand Down Expand Up @@ -221,7 +223,7 @@ func (tail *Tail) reopen() error {
if os.IsNotExist(err) {
tail.Logger.Printf("Waiting for %s to appear...", tail.Filename)
if err := tail.watcher.BlockUntilExists(&tail.Tomb); err != nil {
if err == tomb.ErrDying {
if errors.Is(err, tomb.ErrDying) {
return err
}
return fmt.Errorf("Failed to detect creation of %s: %s", tail.Filename, err)
Expand Down Expand Up @@ -275,7 +277,7 @@ func (tail *Tail) tailFileSync() {
// deferred first open.
err := tail.reopen()
if err != nil {
if err != tomb.ErrDying {
if !errors.Is(err, tomb.ErrDying) {
tail.Kill(err)
}
return
Expand All @@ -284,9 +286,24 @@ func (tail *Tail) tailFileSync() {

// Seek to requested location on first open of the file.
if tail.Location != nil {
_, err := tail.file.Seek(tail.Location.Offset, tail.Location.Whence)
if err != nil {
tail.Killf("Seek error on %s: %s", tail.Filename, err)
offset := tail.Location.Offset
if tail.Location.Whence == io.SeekEnd && offset < 0 {
ret, err := tail.file.Seek(0, io.SeekEnd)
if err != nil {
_ = tail.Killf("Seek error on %s: %s", tail.Filename, err)
return
}

// if ret > abs(offset), use offset
// otherwise, use ret

if ret < int64(math.Abs(float64(offset))) {
offset = -ret
}
}

if _, err := tail.file.Seek(offset, tail.Location.Whence); err != nil {
_ = tail.Killf("Seek error on %s: %s", tail.Filename, err)
return
}
}
Expand All @@ -312,7 +329,7 @@ func (tail *Tail) tailFileSync() {
if cooloff {
// Wait a second before seeking till the end of
// file when rate limit is reached.
msg := ("Too much log activity; waiting a second before resuming tailing")
msg := "Too much log activity; waiting a second before resuming tailing"
offset, _ := tail.Tell()
tail.Lines <- &Line{msg, tail.lineNum, SeekInfo{Offset: offset}, time.Now(), errors.New(msg)}
select {
Expand Down Expand Up @@ -346,7 +363,7 @@ func (tail *Tail) tailFileSync() {
// implementation (inotify or polling).
err := tail.waitForChanges()
if err != nil {
if err != ErrStop {
if !errors.Is(err, ErrStop) {
tail.Kill(err)
}
return
Expand All @@ -359,7 +376,7 @@ func (tail *Tail) tailFileSync() {

select {
case <-tail.Dying():
if tail.Err() == errStopAtEOF {
if errors.Is(tail.Err(), errStopAtEOF) {
continue
}
return
Expand Down